FIG. 1 shows a conventional electroluminescent device 100 having one or more OLED cells. An OLED cell includes a functional stack of one or more organic functional layers 110 between a transparent conductive layer 105 (e.g., indium tin oxide or ITO) and a conductive layer 115. The conductive layers serve as electrodes. The cells are fabricated in an active region 185 on a substrate 101. The cells can be configured as desired to form a display or lamp. A metallization layer which forms interconnections to the electrodes and bond pads 150 is provided. The bond pads are coupled to, for example, driving circuitry to control the operation of the OLED cells. A cap 160 encapsulates the device, hermetically sealing the OLED cells to protect them from the environment (e.g., moisture and/or air.)
The organic functional layer comprises, for example, a conjugated polymer which is dissolved in a solution. The polymer is deposited on the substrate by, for example, spin-coating or doctor blading techniques or other deposition/printing techniques. Generally, the organic layer is relatively thin, for example, about 50–400 nm. Since the organic layer is very thin, small deviations or non-uniformity in the layer can result in optical defects in device operation.
The organic layer coats the glass substrate which is prepared with patterned structures, such as metal interconnection and ITO electrode structures. The various structures create an uneven topography on the substrate surface. The various materials beneath have different surface energies, which, along with the substrate topography, make it difficult to provide a uniform organic layer.
To improve coating uniformity in the organic layer, various solutions have been proposed. Such solutions include, for example, treating the surface of the substrate by oxygen or plasma, selecting suitable metals to which the organic material exhibits good coating behavior, or modifying the organic material to produce good coating properties. However, such solutions have been ineffective because the good coating properties of the organic material is achieved by sacrificing manufacturability which results in higher manufacturing cost and/or performance degradation.
As evidenced from the above discussion, it is desirable to provide a uniform organic functional layer in organic devices, without adversely impacting device performance or increasing cost of manufacturing.